1. Field of the Invention
The present invention relates to a semiconductor manufacturing apparatus for manufacturing semiconductor devices such as various semiconductor memories and central processing units, and more specifically, relates to a plasma processing apparatus for etching the surface of a sample to be processed which is a semiconductor substrate such as silicon using plasma to create a pattern illustrated thereon via lithography technique, so as to form a desired shape on the surface of the semiconductor substrate.
2. Description of the Related Art
Semiconductor devices are manufactured in a plasma processing apparatus by etching the surface of semiconductor substrates using plasma to the shapes of patterns illustrated thereon via lithography technique. In the current state, it is necessary to form patterns with processing dimensions in the order of tens of nm smaller than 0.1 μm via the plasma process, which requires a processing accuracy of a few nm in the order of atomic and molecular sizes. It is predicted that the demand of processing accuracy will become more and more severe in the future. In order to realize such severe processing accuracy with high reproducibility, the plasma conditions must have high stability and reproducibility, and the processing conditions must be controlled through accurate recognition of the progress status of the etching process. In the prior art, accuracy was achieved by accurately reproducing plasma generating parameters such as electromagnetic wave power for discharge, material gas flow rate, material gas pressure and wafer bias power, which are plasma generating conditions optimized in advance. Recently, as disclosed in Japanese Patent Application Laid-Open Publication No. 2006-216605 (patent document 1), in order to realize an even higher processing accuracy, the plasma conditions is observed and the change in status thereof is used to perform feedback control of the plasma generating parameters by which a higher stability is achieved. Moreover, Japanese Patent Application Laid-Open Publication Nos. 61-171130 (patent document 2), 61-53728 (patent document 3) and 1-231325 (patent document 4) disclose observing the processing status of the surface of the sample to be processed via spectroscopic analysis of plasma emission, monitoring the end point and the like of etching and performing accurate process progress control so as to stabilize the processing accuracy.
In order to improve the processing accuracy of the etching process using plasma, it is inevitable to recognize the plasma conditions by monitoring the plasma emission and to perform plasma control by recognizing the status of progress of etching, as described above. It is advantageous to observe the plasma emission from an opposite side from the sample to be processed from viewpoints of detection sensitivity and the like. Especially, it is inevitable to perform observation from the opposite side from the sample to be processed in order to monitor the plasma distribution in real time using the plurality of photodetecting means as disclosed in patent document 1. However, multiple layers of thin films are formed on the silicon substrate which is the surface of the sample to be processed, and plasma emission is reflected by the multiple thin film layers causing interference thereof, so that the change in emission intensity accompanying this interference phenomenon is detected if emission is detected at the opposite side from the sample to be processed, according to which the change in emission intensity intrinsic to plasma cannot be monitored accurately and the control accuracy is deteriorated.